1. Field of the Invention
The present invention relates generally to the field of oxygen barrier polymers. More particularly, it concerns blends of oxygen barrier polymers, such as poly(ethylene/vinyl alcohol) (EVOH), polyvinyldichloride (PVDC), polyethylene terephthalate (PET), or polyamide other than MXD6, with oxygen scavenging polymers, methods of making the blends, packaging articles comprising the blends, and methods of making the packaging articles.
2. Description of Related Art
It is well known that limiting the exposure of oxygen-sensitive products to oxygen maintains and enhances the quality and shelf-life of the product. For instance, by limiting the oxygen exposure of oxygen sensitive food products in a packaging system, the quality of the food product is maintained, and food spoilage is avoided. In addition such packaging also keeps the product in inventory longer, thereby reducing costs incurred from waste and restocking. In the food packaging industry, several means for limiting oxygen exposure have already been developed, including modified atmosphere packaging (MAP), vacuum packaging and oxygen barrier film packaging. In the first two instances, reduced oxygen environments are employed in the packaging, while in the latter instance, oxygen is physically prevented from entering the packaging environment.
Another, more recent, technique for limiting oxygen exposure involves incorporating an oxygen scavenger into the packaging structure. Incorporation of a scavenger in the package has been mainly used to remove headspace oxygen within the package in a short period of time, thus the oxygen scavenging polymer typically is based on the polymer type of high oxygen transmission rate, which ensures that the headspace oxygen in the package quickly reach the oxygen scavenging site and the oxygen level be reduced in a short period of time.
Oxygen barrier polymers, such as poly(ethylene/vinyl alcohol) (EVOH), polyethylene terephthalate (PET), polyvinyldichloride (PVDC), and polyamide, whether cast, blown, or oriented, are widely known for having very strong barrier properties to gases (such as O2 and CO2) and other fluids, and have found wide use in packaging applications where barrier properties are desired. However, it is generally held that their oxygen barrier properties are not as strong as those of traditional packaging materials, such as glass or metals, which latter materials are suitable for packaging applications which require high oxygen barrier properties over a long period of time, such as beer packaging. This requires that the oxygen barrier performance of the existing barrier polymers be significantly improved or their performance approach to those of e.g. glass or metals.
Therefore, it would be desirable to have a packaging article comprising an oxygen barrier polymer and an additional component or components, which packaging article would be better suited for providing a high oxygen barrier over a long period of time than are packaging articles currently known.
Cochran et al., U.S. Pat. No. 5,021,515, discloses a layer of a packaging article comprising 96% polyethylene terephthalate, 4% nylon MXD6, and 200 ppm cobalt.
Paleari et al., U.S. Pat. No. 6,063,417, discloses a packaging film comprising a core layer comprising about 40 wt % to about 85 wt % nylon 6/12, and about 15 wt % to about 60 wt % ethylene/vinyl alcohol copolymer (EVOH).
Koyama et al., U.S. Pat. No. 5,153,038, discloses a packaging article comprising a layer comprising an oxygen scavenger, such as a polyhydric phenol, and a gas barrier resin, such as EVOH or polyamide.
Hong et al., U.S. Pat. No. 5,281,360, discloses a blend of (i) a polymer, such as a formable polyester or polycarbonate; (ii) an oxygen barrier material, such as EVOH, aromatic or aliphatic nylon, or amorphous nylon (including, according to Hong et al., nylon MXD6); and (iii) a transition metal catalyst. If component (ii) is nylon MXD6, it can be present up to about 30 wt % of the blend, with component (i) being, preferably, polyethylene terephthalate (PET).
Collette et al., U.S. Pat. No. 5,759,653, discloses a blend of PET with an oxygen scavenger, such as nylon MXD6. The blend may also further comprise a metal catalyst.
Bacskai et al., U.S. Pat. No. 5,641,825, discloses compositions comprising (i) a polyolefin grafted with an unsaturated carboxylic acid or an unsaturated carboxylic anhydride, (ii) nylon MXD6, and (iii) cobalt as an oxidation catalyst.